374 THE HUMAN ItODY. 



elastic, and moreover, its capillary network when filled with 

 blood will distend it. If its plain muscular layer contracts 

 and compresses it, causing its central lacteal to empty into 

 vessels lying deeper in the intestinal wall, the villas will 

 actively expand again so soon as its muscles relax. In so 

 doing it cannot fill its lacteals from the deeper vessels on 

 account of the valves in the latter, and, accordingly, must 

 tend to draw into itself materials from the intestines; much 

 like a sponge re-expanding in water, after having been 

 squeezed dry. The liquid thus sucked up may draw oil-drops 

 with it, into the free ends of the cells and between them ; and 

 by repetitions of the process it is possible that considerable 

 quantities of liquid, with suspended oil-drops, might be car- 

 ried into the epithelial cells covering a villus. The bile 

 moistening the surface of the villus may facilitate the passage 

 of oil, and it is also said to stimulate the contractions of the 

 villi; if so, its efficacy in promoting the absorption of fats 

 will be explained, in spite of its chemical inertness with re- 

 spect to those bodies. There is also reason to believe that a 

 good deal of the emulsified fat is also directly picked up by 

 amoeboid corpuscles, which push their way between the 

 epithelial cells and thrusting processes into the intestine, pick 

 up oil-droplets, and then travel back and convey their load 

 to the lacteal. 



The path taken by peptones is uncertain. They seem to 

 be very rapidly converted into proteids (? serum albumin) after 

 absorption as they cannot be found, or only traces of them, 

 in the thoracic duct or the portal vein blood of a digesting 

 animal. Moreover, peptones directly injected into the blood 

 are poisonous. Probably they are seized upon 

 formed by the cells of the lymphoid tissue. 



Digestion in the Large Intestine. The contractions of 

 the small intestine drive on its continually diminishing con- 

 tents until they reach the ileo-colic valve, through which 

 they are ultimately pressed. As a rule, when the mass enters 

 the large intestine its nutritive portions have been almost 

 entirely absorbed, and it consists merely of some water, with 

 the indigestible portion of the food and of the secretions of 

 the alimentary canal. It contains cellulose, elastic tissue, 

 mucin, and somewhat-altered bile pigments; some fat if a 

 large quantity has been eaten; and some starch, if raw vege- 

 tables have formed part of -the diet. In its progress through 



